1. Field of the Invention
The present invention relates to an induction heating cooking apparatus. More specifically, the present invention relates to an apparatus for controlling an inverter depending on a load state or a load kind in an induction heating cooking apparatus.
2. Description of the Prior Art
An induction heating apparatus obtains a ripple voltage source by rectifying a commercial alternating current voltage source or further obtains a direct current voltage source by smoothing the ripple current. An inverter circuit is energized by the ripple voltage source or the direct current voltage source, whereby high frequency oscillation is performed with the frequency of approximately 20 to 40 kHz. A high frequency current from the inverter circuit is applied to an induction heating coil, whereby a high frequency alternating magnetic field is generated from the induction heating coil. The alternating magnetic field from the induction heating coil is applied to a load being heated such as a cooking pan disposed in the vicinity of the coil, so that the load is induction heated. As such cooking pan, a pan made of metal including at least iron as the constituent is used. One example of such induction heating cooking apparatus is seen in, for example, U.S. Pat. No. 3,781,503, issued Dec. 25, 1973 to Harnden, Jr. et al. and entitled "SOLID STATE INDUCTION COOKING APPLIANCES AND CIRCUITS"; U.S. Pat. No. 3,781,506 issued Dec. 5, 1973 to Ketchum et al. and entitled "NON-CONTACTING TEMPERATURE MEASUREMENT OF INDUCTIVELY HEATED UTENSIL AND OTHER OBJECTS"; and so on.
Since such induction heating cooking apparatus is not of a type for heating a load being heated using a flame, it is impossible to discern whether the apparatus is in a heating operation only through a look at it. Therefore, there is a fear that a heating operation is started without a load being heated such as a cooking pan being placed on a base or a top plate. There is also a fear that a load smaller than a cooking pan such as a knife, fork or the like is placed on a top plate, without noticing that the apparatus is already in a heating operation, whereby such small load is undesirably heated. In the former case, it is feared that electrical components of the cooking apparatus are damaged, while electric power is wastefully consumed. On the other hand, in the latter case, there could be a risk that the user touches an undesirably heated knife or the like through inadvertence to get burnt in the hand, which is not much preferred from the standpoint of safety. In order to cope with the above described problems, therefore, it has been conventionally proposed that a magnet is disposed beneath the top plate to detect whether a proper load is placed on the top plate, thereby to enable an induction heating operation only when a proper load is placed. Nevertheless, such a conventional approach of detecting presence or absence of a proper load with a magnet entails another problem that the approach cannot be employed in case of a cooking pan made of a special stainless material which is not attracted by a magnet, although such cooking pan serves as a load of an induction heating cooking apparatus.